The engine compartment of a motor vehicle generates a large amount of noise due to the operation of an internal combustion engine.
To reduce the emission of sound to the outside of the vehicle, it is known to line the inside face of the hood with sound insulation and to place a screen beneath the engine to absorb sound emission and prevent engine noise from propagating to the outside of the vehicle by reflection on the roadway.
Those measures have very significant attenuating effects on the emission of engine noise to the outside of the vehicle, but they are not totally satisfactory since internal combustion engine vehicles remain quite noisy in city traffic.
The authors of the present invention have set out to find the causes of this nuisance and have established that the openings that are to be found in the vicinity of the passages for the wheels on either side of the engine compartment constitute non-negligible sources of leakage, contrary to previously-held opinion.
Thus, the inventors have established that each side region of the engine compartment lying between a fender support and the side rail situated on the same side of the vehicle needs to be made proof against noise in order to make the vehicle significantly less noisy, and in particular this needs to be done in the side region of the engine compartment which is not covered by the fender because of the presence of a clearance volume for accommodating vertical travel of a wheel.
In the invention, the term “fender support” is used to designate the part of the structure of a vehicle that performs the function of supporting the fender. This part is sometimes also referred to as “fender lining reinforcement”, “scuttle reinforcement”, or indeed “top side rail”. Similarly, the side rail is sometimes also referred to as a “side member”.
In addition to the region of the engine compartment extending between the fender support and the side rail, the inventors have identified other sources of leaks, including:                the orifice for passing the transmission shaft;        the orifice for passing the rack bar;        the orifice for passing the anti-roll bar;        the orifice for passing the suspension triangle;        the orifice for passing the shock absorber;        the clearance present between the hood and the front fender; and        the clearance between the headlight and the front fender.        